Originally the area of the Forum was humid and covered in grass, as it was not suitable for construction. This changed in the 7th century with the construction of the Cloaca Maxima. This sewer system was based on a natural stream, which was enclosed and covered to drain the area, a sign that the settlements on the Palatine Hill was spreading into the valley.Gradually more public buildings were build around the square, thus forming a natural centre for the rapidly growing town.
In republican times the construction on the Forum continued, with a series of basilicas, notably the Basilica Sempronia and the Basilica Aemilia.
The current image of the Forum Romanum is a result of the changes made by Julius Caesar as pontifex maximus and dictator, which included the construction of the Basilica Julia where the Basilica Sempronia stood, the building of a new Curia and the renovation of the Rostra, the speakers platform. Caesar didn't see all his plans realised before his death, but most was finished by his successor Augustus, including the Temple of Divus Julius, dedicated to Caesar deified.
In imperial times the importance of the Forum as a political centre diminished, but it remained a centre of commerce and religious life. Construction and restoration continued, but now mostly in the form of honorary monuments, such as the Arch of Augustus, the Arch of Titus and the Arch of Septimius Severus.
The Column of Phocas was the last monument to be erected in the Forum in 608 CE, but at this time the area was already half in ruin.
The Forum Romanum suffered damage and destruction repeatedly. When political strife in republican times deteriorated into violence, the Forum would regularly be the scene of fierce fights between rivalling factions, often followed by destructive fires. Later the Forum suffered destruction and pillage at the hands of invaders. Most of the buildings on the Forum was destroyed completely in 410 CE, when the Ostrogoths of Alaric sacked the town.
After the fall of the empire in the west, the area was abandoned. A few buildings were converted into churches, including the Curia, the Temple of Antoninus and Faustina and the Temple of Divus Romulus; the rest was left to shepherds and their animals, to the extent that the popular name of the area became Campo Vaccino, the cattle field.
Archaeological excavations began in 18th century, but the site have only been excavated systematically in the 20th century. Many of the later additions to buildings and monuments have now been removed and the original street level has been restored over large parts of the Forum.
The site of the Forum Romanum is still subject to excavations, and several parts of the Forum cannot be visited, but the whole area have the status of an archaeological site, open to visitors.